The present invention is directed to a particle separating apparatus which employs a grid or screen deck to separate the larger sized particles from a more or less continuous flow of particles of randomly varying size by directing the flow of particles onto the top of a grid or screen deck which is sized to permit the smaller particles to pass through the perforated grid while retaining the larger particles (overs) on the top of the grid, a process frequently referred to as a scalping (separating) operation.
The present invention is especially well adapted for use in a metal chip processing system employed to reclaim machining metal chips produced by mass production machining operations, such as production lines employed to machine finish parts such as engine blocks, heads, valve bodies, transmission cases, etc. on a mass production basis. Many of these parts today are being made of aluminum or other metals whose intrinsic value is such as to justify a fairly substantial investment in equipment for processing and reclaiming chips generated in the machining operation.
A typical chip processing system finds the metal chips collected at all of the various machine tools being conveyed or transferred to a common collection point representing the inlet end of the chip processing system. In that typically the collected chips are produced by several different types of machining operations, the chip sizes and shapes can vary over a substantial range, and most chips when initially collected will be coated with cutting oils or coolants employed during the machining operation. In addition to the chips themselves, many shop workers view the chip bins or collection receptacles as convenient places to discard metal objects such as broken tools, spoiled/damaged parts, etc., these objects being generally referred to as tramp metal. Chip processing systems typically clean and dry the chips and the processing equipment employed, while designed to handle a wide range of particle sizes, tends to be clogged, jammed or obstructed by the larger particles, particles which may tend to cling to each other in bundles, and tramp metal of the type referred to above. Thus, the initial step of the chip reclamation process is to separate tramp metal, chip bundles and large particles in excess of a selected size to avoid the foregoing problems with downstream processing equipment. Typically, this is accomplished by dumping the particles upon a perforated horizontal vibrating screen deck which allows the smaller particles to pass downwardly through the screen onto a conveying device which feeds the passed particles into the processing chip equipment system. Particles too large to pass through the screen openings are collected on top of the screen as "overs" and periodically manually removed. In some cases the "overs" are passed through a hammer mill or other device which reduces the size of the particle bundles to sizes which may be handled efficiently by the chip processing equipment and/or discarded and recycled by other processing means.
The chips produced by machining operations typically will have sharp jagged "fish hook" edges and thus tend to interlock or cling to other chips to produce chip bundles or hooked necklasses which may be of a size large enough to be retained on the top of the screen, even though the individual chips which make up the bundle are all much smaller than the screen opening. Other chips of relatively small size may fall upon the screen on top of larger chips and be retained against passage through the screen due to blinding. To induce these smaller (selected size) chips to pass through the screen, in some instances the screen is vibrated in an attempt to sift the smaller particles through the screen as by breaking up the hooked chip neckless bundles and shaking smaller particles loose from the bundles. However, large dynamic variations to supporting structures and limits to deck length due to the need to drive the screen deck at the center of gravity are the limiting factors on conventional screens (vibrating type).
In that the smaller particles which pass through the screen drop freely from the underside of the screen, the most convenient way to collect these particles is in a trough underlying the screen, and hence a conveying screw or auger operating in the bottom of the trough is the most common device employed to advance chips which pass through the screen to the next stage of the chip processing system. While conveying augers of this type are efficient and well adapted for this use, where metal particles are involved, the auger has one inherent characteristic which will cause problems. This is the fact that rotation of the auger causes that portion of the conveying flight on one side of a vertical plane containing the auger shaft axis to move upwardly while the portions of the conveying flight on the opposite side of that vertical plane must move downwardly. The trough side walls are inclined downwardly toward opposite sides of the auger to pass beneath the auger with a relatively small operating clearance between the trough and the lower portions peripheral edge of the conveying flight of the auger. On that side of the auger which is moving downwardly, particles are pushed both forwardly and downwardly by the flight into a conveying nip between the edge of the converging flight and the trough wall, this side of the flight being frequently referred to as the "pinch" side of the auger. Where relatively hard metal chips (solids) are involved, the chips/solids can become pinched or jammed between the conveyor auger flight and trough wall. This condition will overload the auger drive equipment motor and stall the screw auger rotation.
The present invention is directed to a scalping grid or screen deck which may be driven in a horizontal vibratory movement induced by the rotating conveying screw auger and in which pinching or jamming of the fixed machine conveyor screw or auger is minimized or eliminated by an integral shelf rigidly attached below the screen/deck.